4B.6 What is RKW Theory?

Monday, 5 November 2012: 5:30 PM
Symphony II (Loews Vanderbilt Hotel)
George H. Bryan, NCAR, Boulder, CO
Manuscript (352.9 kB)

"RKW Theory" is the nickname for the concepts presented by Rotunno, Klemp, and Weisman in the 1980s. Originally presented as “A Theory for Squall Lines” (Rotunno et al. 1987), the title of the work was modified slightly to “A Theory for Strong, Long-Lived Squall Lines” for the peer-reviewed journal article, Rotunno et al. (1988; hereafter RKW88).

Like all scientific concepts, RKW Theory has been subjected to revision and refinement by subsequent studies. Perhaps the most significant revisions to RKW Theory came in the article by Weisman and Rotunno (2004; hereafter WR04), although according to WR04 the "basic interpretations of the RKW theory are reconfirmed" by their study. Some other studies have challenged this conclusion by WR04.

So, what are "the basic interpretations of the RKW theory"? In an attempt to answer this question succinctly, this presentation focuses on the core concept of RKW Theory: specifically, that a surface-based cold pool acts to accelerate boundary-layer air over the top of the cold pool (which affects squall lines negatively), and that environmental vertical wind shear acts to accelerate boundary-layer air away from the cold pool on its downshear side (which can also affect squall lines negatively), but that these two effects can counteract each other (and thus cold pools in sheared environments can affect squall lines positively). The terms “affect negatively” and “affect positively” address whether new deep precipitating convection is initiated in roughly the same system-relative region throughout time, which is necessary for a squall line to achieve its definition of "a line of active thunderstorms" (AMS Glossary). Hence, it is argued in this presentation that RKW Theory is probably best thought of as "A Theory for Squall Line Structure." The additional words in the title of RKW88 --- i.e., "strong, long-lived" --- seem to have focused the severe storm community's attention toward subcomponents of RKW Theory, such as the theoretical squall-line structure that yields the strongest possible ascent, i.e., the "optimal" state for squall lines.

The presentation will conclude with a brief discussion of the aforementioned revisions to RKW Theory. Future studies that evaluate RKW Theory are encouraged to incorporate these revisions in their evaluation.


Rotunno, R., J. B. Klemp, and M. L. Weisman, 1987: A theory for squall lines. Preprints, 3rd Conference on Mesoscale Processes, Vancouver, B.C., Canada, Amer. Meteor. Soc., 2-3.

Rotunno, R., J. B. Klemp, and M. L. Weisman, 1988: A theory for strong, long-lived squall lines. J. Atmos. Sci., 45, 463-485.

Weisman, M. L., and R. Rotunno, 2004: “A theory for strong long-lived squall lines” revisited. J. Atmos. Sci., 61, 362-382.

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